Stalagmite is an excellent archive for reconstructing climate conditions in temperate-tropical areas. Our previous study reconstructed Holocene temperature changes at high resolution from a well-dated stalagmite (KA01) in the Kiriana Cave in Mie Prefecture, Japan, but could not extract information related to precipitation change. Here, the δ13C and Mg/Ca ratio of KA01 were used to discuss the precipitation variability. These proxies reflect prior calcite precipitation (PCP; calcite precipitation before the water reaches a stalagmite), which can be used to evaluate the precipitation. The δ13C-based PCP with higher time resolution indicates a humid interval of 9.8–7.2 ka and dry intervals of 12.3–13.3 and 4.0–2.0 ka. These humid and dry intervals broadly correspond to the warm and cold intervals, respectively, which were identified in our previous study. This correspondence may have resulted from the oceanographic change in the northwest Pacific, which is dominant moisture and heat sources for the study area. The humid-warm conditions during 9.8–7.2 ka were unstable, with short-term dry and cold periods. The dry and cold period around 8 ka may correspond to the global “8.2 ka event”. The cold-dry period of 4.0–2.0 ka corresponds to the late Jomon period when the population in the Japanese Islands declined. The cold-dry climate is suggested as one of the possible causes for the population decline, and may have spread across a wide area of the Japanese islands. Due to global warming, the future climate along the Pacific coastline is expected to resemble the conditions of the warmest interval in the early-middle Holocene. Considering the high precipitation during this interval, future warming will be accompanied by an increase in precipitation. (273 letters).
Lake Funazoko-Ike was formed by a relative sea level fall due to crustal uplift after the melting of the ice sheet. Today, the lake surface lies approximately 25 m below the present sea level. Evidence of these processes is recorded in sediments deposited from the sill to the lake surface around Lake Funazoko-Ike during the middle to late Holocene. A total of 123 sediment samples were collected from outcrops of the Holocene-raised beach around Lake Funazoko-Ike in Skarvsnes, Antarctica, during geomorphological surveys by the 38th and 46th Japanese Antarctic Research Expeditions (JARE38 and JARE46). The samples were analyzed for grain size, carbon, nitrogen, and sulfur (CNS) contents, as well as microfossil assemblages, including arenaceous foraminifera and siliceous microfossils. Radiocarbon dating of marine fossils yielded ages ranging from approximately 4100 to 800 cal. yr. BP. From six samples, we identified at least 54 species belonging to 29 genera of siliceous microfossils. Arenaceous foraminifera were identified in one additional sample. Three sea-ice indicator diatom taxa were dominant in all six samples. These results suggest that Lake Funazoko-Ike was in an open marine environment from approximately 4100 to 1200 cal. yr. BP. The lake became isolated from the sea sometime between 800 and 1200 cal. yr. BP. This timing aligns with the isolation of the coastal margin in northwest Skarvsnes, providing evidence to understand spatial and temporal variations in ice sheet dynamics during the Holocene.
Subduction tectonics related to Late Paleogene island-arc magmatism in Northern Luzon, the Philippines, has been debated for some time. New field data, combined with zircon U–Pb dating and Hf isotopic studies, whole-rock element and Nd isotopic data from the Caraballo Formation in the Northern Sierra Madre reveal two suites of island-arc magmatic rocks: (1) ~34 Ma igneous rocks characterized by low-K2O (≤ 0.6 wt.%), low Nb/Yb (0.11–0.26), and high 143Nd/144Nd (εNd[t] = 9.5–9.9), and (2) ~31 Ma igneous rocks exhibiting progressive enrichments of K2O (~0.8 wt.%), Nb/Yb (0.37–0.76), and 143Nd/144Nd (εNd[t] = 8.2–9.1). These differences reflect a shift in subduction influences, transitioning from slab fluids of an old subducted slab to slab melts with adakitic characteristics of young subducted slab between 34 and 31 Ma. The ~46 Ma Dupax Batholith in the Caraballo Mountains shows similar geochemical and isotopic signatures as the ~34 Ma igneous rocks of the Caraballo Formation (K2O: ~0.7 wt.% vs. ≤ 0.6 wt.%; Nb/Yb: 0.24 vs. 0.11–0.26; zircon εHf[t]: 13.8–15.8 vs. 13.7–15.7). This suggests a similar mantle source and subduction influx in both cases. When considered in conjunction with available geochronological and geochemical data from the Northern Sierra Madre, the Caraballo Mountains, and the Central Cordillera, this suggests that arc growth of Northern Luzon may have started as early as the Middle Eocene. The eastern and western ranges of Northern Luzon comprised the Proto-Luzon Arc before the intra-arc rifting started in the Late Oligocene–Early Miocene. Unlike a Neogene cessation of island-arc magmatism in the Northern Sierra Madre, there was a persistent arc growth in the Central Cordillera. It suggests that the Central Cordillera always situated in the frontal arc while the Northern Sierra Madre evolved from a Late Paleogene back arc to a Neogene remnant arc. This supports a continuously east-dipping subduction along the western plate boundary of Northern Luzon. We conclude that the change of subduction influence in the Northern Luzon Arc during the Middle Eocene to Early Oligocene is linked to the migration of the subducted slab from the Mesozoic Eastern Neo-Tethys to the Eocene Celebes at ~31 Ma.
The present investigation proposes the first geodynamic model to explicate the intricate relationships among the recently reported high Mg-andesites (HMAs) and rhyolites along with the associated metadolerites and granites related to the Shillong back-arc basin (1900–1400 Ma) of the Assam-Meghalaya Gneissic Complex (AMGC), Northeast India. This model aims to provide critical insights into the complex subduction geodynamics, magmatic processes, and crust–mantle interactions that occurred in the AMGC when the South Indian Block subducted beneath the North Indian Block along the Central Indian Tectonic Zone (CITZ) during the Columbia supercontinent amalgamation. The genesis of the HMAs is attributed to the lithospheric mantle, which underwent metasomatism via an influx of exceedingly higher degree of sediment-derived fluids originating from the subducting slab, while the doleritic melt is sourced from a mixed lithospheric-asthenospheric mantle, where slab-derived fluids with a lower sediment flux facilitated the decompression melting of the upwelling asthenosphere, leading to the generation of mafic magma at deeper mantle depths. The rhyolites are characterized as A-type in nature, giving an average zircon saturation temperature of 842°C. They were generated through underplating of the high-temperature mafic magma beneath the crust, which induced substantial thermal flux, driving crustal anatexis and the generation of A2-type felsic magma in the back-arc setting. The basin's geodynamic significance is corroborated by its complex metamorphic and polyphasic deformational history. Geothermobarometric calculations involving the metadolerites yielded pressure–temperature estimates of 5.62–8.64 (average 7.02) kbar and 655–701 (average 683)°C, which assign an amphibolite facies metamorphism to these rocks, remnants of their peak metamorphic conditions during the Pan-African tectono-thermal episode (~500 Ma). Our postulated geodynamic model for the Paleo-Mesoproterozoic Shillong Basin of the AMGC, which we consider as the easternmost continuation of the CITZ, carries substantial significance in comprehending the broader geodynamic scenario operative during the creation of the Greater Indian Landmass during the Proterozoic.
Metamorphosed pelitic and psammitic rocks with small amounts of granitic stock are found on Ozushima Island, in the Seto Inland Sea area of Yamaguchi Prefecture, Japan. The metamorphosed pelitic rocks exhibit pervasive foliation defined by the preferred orientation of muscovite, biotite, andalusite, and sillimanite. General foliation shows an E–W trend and dips to the north and south, forming upright folds. The mineral assemblages and microstructures reveal that the metamorphic rocks of Ozushima Island can be divided into the Bt zone, And zone, and Sil zone, representing three metamorphic zones and corresponding to three deformational stages. Based on field surveys, the following deformational events were identified. Stage 1 deformation resulted in S1 foliation parallel to the bedding plane (S0). The critical minerals in each metamorphic zone formed the S1 foliation. In Stage 2, the S2 foliation developed along the axial planes of the microfolding of the S1 foliation. A NW-SE striking, NE-dipping thrust passed through the southern part of the island. In Stage 3, S3 foliation was locally present along the thrust plane. The metamorphic conditions of the And and Sil zones were estimated using conventional geothermobarometers at 530°C, 60 MPa and 600°C–710°C, 330–400 MPa, respectively. In addition, these metamorphic conditions plot within the metamorphic field gradient of the Cretaceous Ryoke metamorphic rocks from the Yanai-Iwakuni and Omuta areas. The detrital zircon grains separated from the psammitic rocks exhibited two age peaks at c. 1800 Ma and c. 250 Ma. A younger age indicates an older limit on the depositional age of the protoliths. These findings suggest that the metamorphic rocks of Ozushima Island originated from the Suo Belt and underwent low-pressure and high-temperature metamorphism, probably caused by heat supplied from the Cretaceous intrusive rocks, similar to the Ryoke metamorphic rocks.
We performed U–Pb zircon dating using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for gneissose and massive granitoids from the Aoyama area, Ryoke belt, Southwest Japan. This is the first comprehensive report of U–Pb zircon ages from the Aoyama area, a key region to discuss an along-arc variation of the lower crustal magma generation in the Ryoke belt. Solidification timings of the Kabuto Granodiorite, Ao Granite, Misugi Tonalite, Joryu Tonalite, and Kimigano Granodiorite are considered to be ca. 80, ca. 72, ca. 74, ca. 88, and ca. 112–99 Ma, respectively. These timings are consistent with published intrusion relationships. Kimigano Granodiorite characteristically gives old magmatic ages, showing the magmatic activity predating the regional high-temperature metamorphism in the Aoyama area. The scattered U–Pb dates indicate either a long duration of zircon crystallization or rejuvenation of U–Pb dates of preexisting zircon grains. Magmatic activities are continuously observed for ~15 Myr, following the ~10 Myr “lull” after the solidification of the Kimigano Granodiorite at ca. 112–99 Ma. There is an ~8 Myr age gap between the youngest gneissose granitoid of the Joryu Tonalite and the oldest massive granitoid of the Kabuto Granodiorite. Zircon grains of the Kimigano Granodiorite and the Joryu Tonalite could be, respectively, affected by regional Ryoke metamorphism and by contact metamorphism due to the intrusion of the adjacent Ao Granite.
Nanayama, F., Yamasaki, T., Kanamatsu, T., Iwano, H., Danhara, T., and Hirata, T. (2022). “Origin and Evolution of the Paleo-Kuril Arc Inferred From Detrital Zircon U–Pb Chronology in Eastern Hokkaido, NE Asia.” Island Arc 31, no. 1: e12458. https://doi.org/10.1111/iar.12458.
In the Supporting Information, Table S4 and Table S5 contained errors. The data intended for Table S5 was mistakenly uploaded in place of Table S4. This has been corrected by restoring the original Table S4 and updating Table S5 with the correct data.
We apologize for these errors.
Intermittent volcanic activity has continued at Nishinoshima volcano in the Izu–Bonin arc in the western Pacific since 2013, characterized mostly by effusive Strombolian eruptions (Episodes 1–3). Subsequently, the eruption style changed suddenly to explosive violent Strombolian in mid-June 2020 (Episode 4), after which the volcano entered a period of quiescence. In 2021, volcanic activity restarted at Nishinoshima, although the eruptions were small (Episode 5). The change in eruption style between Episodes 1–3 and 4 was controlled mainly by a change in magma composition. However, the details of the redox state with respect to magma composition remain unclear. We aimed to understand the change in magma composition during Episode 4 and the subsequent activity, focusing on the redox state. Fe–K edge X-ray absorption near edge structure (XANES) analysis and petrographic observations were performed on volcanic glass in seafloor and subaerial samples from Episodes 4 and 5. The results show that the explosive eruption of Episode 4 was characterized by the intrusion of oxidized basaltic magma into a reduced andesitic magma, which is a similar tendency to another large-scale eruption in the Izu-Bonin arc (Fukutoku-Oka-no-Ba). Episode 5 shows different redox changes, involving remnants of the basaltic andesite magma from Episode 4, whose fO2 had been reduced. The groundmass glass in Episode 5 subaerial ejecta has oxidized and differentiated (SiO2-rich) composition possibly due to the subaerial cooling process. The observed geochemical and petrographic characteristics suggest that the small Episode 5 eruption occurred due to the continuous feed of the magma similar to Episode 4, but the magma plumbing system in the volcano made the provided high fO2 magma reduced, which may mitigate the explosivity of the future eruption.
Pumice is a pyroclastic material of low density and is occasionally buoyant in water. When it erupts from submarine volcanoes, it can drift long distances and wash ashore at remote beaches. Pumice from the eruption of Fukutoku-Oka-no-Ba volcano in the Izu–Bonin arc in October 2021 drifted for about 2 months over a distance of > 1300 km onto the Nansei Islands of Japan, disrupting shipping, fishing, and coastal ecosystems. In March 2024, large amounts of dark brown to black pumice washed ashore on these islands, and subsequently in the Kanto area of Japan. Their geochemical and petrographic characteristics were examined, and Ioto volcano, which is one of the most active volcanoes in Japan, was identified as a possible source based on these characteristics. Small amounts of similar pumice clasts drifting ashore in the Nansei Islands during 2022–2023 were also identified as originating from Ioto volcano. Since July 2022, volcanic activity involving magma eruption has occurred off the southeast coast of Ioto, where pumice rafts generated by the eruptions have been observed. Drift simulations indicate that pumice ejected from Ioto could reach the Nansei Islands, where it is widely distributed. The observation of pumice drifting along the coast of these islands thus provides information on the dispersal of pumice to other parts of Japan, with sources effectively identified through their chemical composition. The results contribute to our understanding of the eruption histories of submarine volcanoes in the Izu–Bonin arc.
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